block: fix a race between del_gendisk and BLKRRPART

When BLKRRPART is called concurrently with del_gendisk, the partitions
rescan can create a stale partition that will never be be cleaned up.

Fix this by checking the the disk is up before rescanning partitions
while under bd_mutex.

Signed-off-by: Gulam Mohamed <gulam.mohamed@oracle.com>
[hch: split from a larger patch]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210514131842.1600568-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: gulams

fs/block_dev.c

@@ -1244,6 +1244,9 @@ int bdev_disk_changed(struct block_device *bdev, bool invalidate)
 
 	lockdep_assert_held(&bdev->bd_mutex);
 
+	if (!(disk->flags & GENHD_FL_UP))
+		return -ENXIO;
+
 rescan:
 	if (bdev->bd_part_count)
 		return -EBUSY;